.box {
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
}
.box:nth-child(1) {
  background-color: rgba(20,5,9,0.1);
}
.box:nth-child(2) {
  background-color: rgba(40,10,18,0.2);
}
.box:nth-child(3) {
  background-color: rgba(60,15,27,0.3);
}
.box:nth-child(4) {
  background-color: rgba(80,20,36,0.4);
}
.box:nth-child(5) {
  background-color: rgba(100,25,45,0.5);
}
.box:nth-child(6) {
  background-color: rgba(120,30,54,0.6);
}
.box:nth-child(7) {
  background-color: rgba(140,35,63,0.7);
}
.box:nth-child(8) {
  background-color: rgba(160,40,72,0.8);
}
.box:nth-child(9) {
  background-color: rgba(180,45,81,0.9);
}
.box:nth-child(10) {
  background-color: #c8325a;
}
.box:nth-child(11) {
  background-color: #dc3763;
}
.box:nth-child(12) {
  background-color: #f03c6c;
}
.box:nth-child(13) {
  background-color: #ff4175;
}
